Sintered blanks

ABSTRACT

The formation of inner and outer bearing rings is described by roll forming to shape a sintered metal blank. The roll forming is found to densify the ring in the bearing areas where high strength is required and also it is surprisingly found that some flow of the metal to give the required final shape can be achieved without fracture of the blank.

United States Patent [191 Connell et a1.

SINTERED BLANKS Inventors: Gordon Sidney Connell,

Cheltenham; Paul Egan, Harescombe, both of England F ormflo Limited,Gloucestershire, England Filed: Oct. 5, 1972 Appl. No.: 296,368

Assignee:

U.S. ..29/148.4 R, 29/1495 PM, 72/366, V 29/42 075 Int. Cl B2111 1/12Field of Search..... 29/4205, 148.4 R, 149.5 R, 29/1495 PM, 182; 72/80,102, 365, 366

References Cited UNITED STATES PATENTS 10/1941 Darby et a1. 29/1495Primary Examiner-Lowell A. Larson Attorney, Agent, or Firm-PolloclPhilpitt & Vande Sande [57] ABSTRACT The formation of inner and outerbearing rings is described by roll forming to shape a sintered metalblank. The roll forming is found to densify the ring in the bearingareas where high strength is required and also it is surprisingly foundthat some flow of the metal to give the required final shape can beachieved without fracture of the blank.

11 Claims, 8 Drawing Figures SINTERED BLANKS This invention relates tothe roll forming of blanks to give inner and outer bearing rings and tothe roll formed bearing rings thus produced.

BACKGROUND OF THE INVENTION Simple shaped articles are often prepared bycompacting and sintering a powdered metal. There are various ways ofpreparing these powder metal articles. According to one method, thepowdered metal is compacted in a mould or die and then sintered. Theresulting articles are very brittle and not particularly strong ordense. Their strength and density can be increased, however, bysubjecting them to further compaction after sintering, optionallyfollowed by further sintering. Alternatively the second compaction canbe effected while the article is still hot.

The making of simple powder metal articles by these procedures enablesone to make simple regular shaped articles relatively cheaply. Oneexample of a simple regular shape which can be made readily and cheaplyis a cylinder.

As noted above these simple shaped powder metal articles are quitebrittle and not particularly dense and so they cannot usually bemachined or shaped in other ways after compaction.

BRIEF DESCRIPTION OF THE INVENTION We have now surprisingly foundaccording to the invention that a substantially cylindrical powder metalblank can be roll formed to give an inner or outer bearing ring.

We believe that the roll forming should be effected in such a way thatinitially the cylindrical powder metal blank is made more dense byfurther compaction and thereafter the metal is caused to flow to thedesired final shape of the bearing ring. We find that, in this way, theexpected problems of brittleness are avoided and that the powder metalblanks can-be formed without fracture. It appears that the ability ofthe blank to flow after compaction is largely dependent upon its densityand ductility.

We also believe that initially the powder metal blank should have arelatively high density. It appears that the density after compactionand sintering and before roll forming should be at least 96 percent, andpreferably about 98 percent, of the density of the solid material.

It apears that the material of the powder metal blank should have a goodductility so as to allow the metal to flow to shape during rollingwithout fracture. Thus it is preferred that the metal have an elongationfactor, i.e., percentage elongation when fracture occurs, of not lessthan 9 percent, with a value in the region of 12 percent is found togive good results.

An important advantage of roll formed bearing rings prepared accordingto the invention is that during the roll forming, work hardening and theconsequential risk of fracture does not appear to occur, or occur toanything like the same extent, as compared with the similar roll formingof a solid blank of the same metal. For example, we find thatcylindrical powder metal blanks of the steel known as EW 31 can be rollformed without fracture, whereas when solid substantially cylindricalblanks of EN 31 are roll formed, they are more susceptible to fracture.

Also the roll formed bearing rings prepared according to the inventionare compacted or given greater density and strength in those regions oftheir surface where greater density and strength are required. Thus theregions of the bearing groove and opposed cylindrical surfaces havegreater density and fatigue strength than other regions of the bearingring.

The substantially cylindrical powder metal blanks for roll forming canbe produced, for example, in any of the ways outlined above and willhave a very accurate shape and size. They are therefore eminentlysuitable for use in the roll forming process without further shap' ingor sizing operations. For example, the powder metal blanks can becylindrical or cylindrical with the flat annular edges chamfered.

The roll forming of the powder metal blanks is likely to produce arolled surface of nearly percent density and so the bearing surfaces ofthe roll formed bearing rings have an excellent polished appearance.

The roll forming of the invention can be effected cold, warm or hot. Inaddition the roll forming can be effected in any convenient way usingknown roll forming apparatus. Examples of suitable roll formingapparatus for roll forming the articles according to the invention areshown in United Kingdom Pat. Applications 63607/69 and 5132/71.

Suitable powder metal blanks for roll forming according to the presentinvention can be made, for example, from those steels having thedesignations SAE 4600, SAE 8600, SAE 52,100, EN 31, EN 32A and EN 24.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be illustratedby way of example, with reference to the accompanying drawings, inwhich:

FIGS. 1A, 1B, 1C and 1D show four stages in the roll forming ofacylindrical sintered metal blank to give an inner bearing ring; and

FIGS. 2A, 2B, 2C and 2D show the equivalent four stages in the rollforming ofa cylindrical wrought metal blank.

DESCRIPTION OF THE PREFERRED EMBODIMENT The cylindrical sintered metalblank 10 is shown mounted on a rotatable mandrel 12 in FIG. 1A and it isto be formed to the shape of an inner bearing ring 14 (FIG. ID) by meansof a suitably profiled forming roll 16. The later has an annular hump 18on either side of which are cylindrical portions 20 beyond which areinclined flanks 22.

At the start of the roll forming operation shown in FIG. 1A, therotating forming roll 16 is advanced to wards the sintered metal blank10 and continued advance causes the annular hump 18 to start to form anannular recess 24 in the blank 10. At the stage shown in FIG. 1B thehump 18 causes further densification of the blank with substantially noflow of metal.

As the forming roll 16 continues to advance towards the mandrel 12 (thestage shown in FIG. 1C) the metal in the region of the recess 24 iscompressed to a density approaching 100 percent of the density of thesolid metal and then a flow of the metal occurs as shown by the arrows26. Continuation of the advance of the forming roll 16 then causesfurther metal flow shown by the arrows 28 and 30 so that the blankspreads to conform to the cylindrical portions 20 and flank 22 of theforming roll. Atthe same time, with width of theblank increases. I l

The finished bearing ring 14 is shown in FIG. 1D. This has been highlyCompressed and densified in the region 32 around the annular recess 24so giving the ring high-strength in that region where the bearing ringwill be subjected to a large loading when in use. The

ring'also has a highly polished and excellent finished rolled surface. a

The roll formingope'ration is only shown diagrammatically in FIGS. 1A to1D. Normally, there will be two diametrically opposed forming rolls 16which progres sively squeeze the blank I"between' them; only one rollhas been shown for the sake of simplicity, however.

By way of contrast the steps of roll forming of a wrought cylindricalblank 40 to give an inner bearing ring are shown in FIGS. 2A to 2D, thestages A to D corresponding'to the stages A to D of FIG. 1.

As shown in FIG. 23, as soon as the roll forming commences, metal flowoccurs as shown by the arrows 42 since the material is already at itsmaximum density. With continued advance of the forming roll 16, themetal flow continues and by stage C width growth of the blank 40 (shownby arrows 44) occurs. The finished ring 50 is achieved at stage D (FIG.2D) and will be appreciated by comparison with FIG. 1, the roll formingof the solid metal cylindrical blank 40 requires a considerable extraflow of metal which of course leads to a greater risk of fracture of themetal during roll forming.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly it is apropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention herein.

What we claim is: l. A method of preparing an inner or outerbearing ringcomprising the steps of:

a. forming a substantially cylindrical sintered powder metal blankhaving a density of at least 96 percent of the density of the solidmetal, and

b. roll forming said blank to the shape of said required inner or outerbearing ring.

2. A method according to claim 1 in which said metal has an elongationfactor of not less than 9 percent.

3. A method according to claim 1 wherein said metal has an elongationfactor in the region of 12 percent.

4. A method according to claim 1 wherein said blank has a density ofabout 98 percent of the density of the solid metal.

5. a method according to claim 4 wherein said metal has an elongationfactor of'not less than 9 percent.

6. A method of preparing a bearing ring comprising:

a. compressing and sintering a powdered metal'in a mould to asubstantially cylindrical blank to a density of at least 96 percent ofthe density of the solid metal,

b. squeezing and rolling said cylindrical blank between profiled formingmembers so as to initially compact parts of said blank and then causeflow of said compacted metal parts to form one or more annular recessesin said blanks so giving said required bearing ring.

7. A method according to claim 6 in which said blank has a density ofabout 98 percent of the density of the solid metal.

8. A method according to claim 6 in. which said metal has an elongationfactor of not less than 9 percent.

9. A method according to claim 8 in which said metal has an elongationfactor in the region of 12 percent.

10. A method according to claim 7 wherein said metal has an elongationfactor of not less than 9 percent.

11. an inner or outer bearing ring manufactured by roll forming asubstantially cylindrical blank of sintered powder metal having adensity of at least 96 percent of the density of the solid metal,comprising:

a cylindrical ring having an annular load bearing recess located on aninner or outer surface thereof, the region of material around said loadbearing recess being compressed and densified to a density approaching100 percent of the density of the solid metal, thereby providing highstrength in said load bearing recess.

1. A method of preparing an inner or outer bearing ring comprising thesteps of: a. forming a substantially cylindrical sintered powder metalblank having a density of at least 96 percent of the density of thesolid metal, and b. roll forming said blank to the shape of saidrequired inner or outer bearing ring.
 2. A method according to claim 1in which said metal has an elongation factor of not less than 9 percent.3. A method according to claim 1 wherein said metal has an elongationfactor in the region of 12 percent.
 4. A method according to claim 1wherein said blank has a density of about 98 percent of the density ofthe solid metal.
 5. a method according to claim 4 wherein said metal hasan elongation factor of not less than 9 percent.
 6. A method ofpreparing a bearing ring comprising: a. compressing and sintering apowdered metal in a mould to a substantially cylindrical blank to adensity of at least 96 percent of the density of the solid metal, b.squeezing and rolling said cylindrical blank between profiled formingmembers so as to initially compact parts of said blank and then causeflow of said compacted metal parts to form one or more annular recessesin said blanks so giving said required bearing ring.
 7. A methodaccording to claim 6 in which said blank has a density of about 98percent of the density of the solid metal.
 8. A method according toclaim 6 in which said metal has an elongation factor of not less than 9percent.
 9. A method according to claim 8 in which said metal has anelongation factor in the region of 12 percent.
 10. A method according toclaim 7 wherein said metal has an elongation factor of not less than 9percent.
 11. an inner or outer bearing ring manufactured by roll forminga substantially cylindrical blank of sintered powder metal having adensity of at least 96 percent of the density of the solid metal,comprising: a cylindrical ring having an annular load bearing recesslocated on an inner or outer surface thereof, the region of materialaround said load bearing recess being compressed and densified to adensity approaching 100 percent of the density of the solid metal,thereby providing high strength in said load bearing recess.